The present invention relates generally to radioactive source wires used to irradiate body tissue in the treatment of disease. More particularly, the present invention relates to the use of an elongated radioactive source wire with increased flexibility for the localized delivery of radiation to diseased tissue.
The most common cause of death in industrial countries is ischemic heart disease which, generally speaking, is an imbalance between myocardial oxygen supply and demand. This imbalance is most often due to obstruction of large coronary arteries by sclerotic plaque and is related to either an absolute decrease in coronary blood flow or an inability to increase coronary blood flow relative to the needs of the heart. Ischemic heart disease is most commonly associated with chest pain, an acute heart attack, an abnormal ventricular rhythm and sudden death. Although various medical and surgical therapies may improve the quality of lifestyle of many patients with this disease, these therapies do not favorably change the underlying cause for the coronary vessel narrowing, nor do they stop its progression.
Various medical interventions have been employed to remove or otherwise treat an offending occlusion in the heart including transluminal angioplasty, coronary artery bypass grafting (CABG), balloon angioplasty, stents, and atherectomy. Of these, balloon angioplasty is the procedure of choice and also the least invasive alternative.
In the past, catheters have been developed which may be effectively inserted into blood vessels and maneuvered through a vascular tree. A balloon may be used with such catheters to expand inside the vessel and to open blockages found therein. In a typical percutaneous transluminal coronary angioplasty (PTCA) or percutaneously transluminal angioplasty (PTA) procedure, a guiding catheter is percutaneously introduced into the vascular system of a patient through an artery and advanced therein until the distal tip of the guiding catheter is appropriately positioned. A dilation catheter having a balloon on the distal end thereof and a guide wire are slidably disposed and introduced through the guiding catheter. The guide wire is first advanced through the distal tip of the guiding catheter until the distal end of the guide wire crosses the lesion to be dilated. The dilation catheter is then advanced over the previously introduced guide wire until the dilation balloon on the distal extremity of the dilation catheter is properly positioned inside the lesion. The balloon portion of the dilation catheter is then inflated to a predetermined size to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall to thereby reduce the annular stenosed area. After a period of time, the balloon is deflated so that blood flow is resumed, allowing the dilation catheter to be removed.
A major problem encountered in a significant number of patients treated by this procedure is the subsequent narrowing of the artery after the expansion treatment. Various methods and apparatus have been developed to address the restenosis problem including multiple inflations of the balloon during the original procedure, atherectomy, hot balloons, and lasers. Even the installation of permanent stents has been thought to potentially have some value in reducing restenosis rates. See, for example, U.S. Pat. No. 5,019,075 to Spears et al. wherein the region surrounding the balloon utilized in the angioplasty procedure is heated by means within the balloon, or within the skin of the balloon, upon inflation of the balloon in order to ideally fuse together fragmented segments of tissue. U.S. Pat. No. 4,733,655 to Palmaz discloses an expansible vascular graft which is expanded within a blood vessel by an angioplasty balloon to dilate and expand the lumen of the blood vessel. The Palmaz method and apparatus leaves the expandable vascular graft in place to ideally prevent recurrence of stenosis in the body passageway.
However, recent data seems to indicate that the prior art methods described above do not significantly reduce restenosis rates of occurrence. It would therefore be desirable to have a method and apparatus to treat a lesion in order to reduce the restenosis rate of occurrence. The present invention is believed to provide a unique method and apparatus to reduce the restenosis rate of occurrence following an angioplasty or like-intended procedure.
As discussed above, percutaneous transluminal coronary angioplasty (PTCA) is now commonly used for opening blockages, also called stenoses, of both peripheral and coronary arteries. However, within a period of several months after PTCA, a significant percentage of treated arteries experience a reoccurrence of the narrowing, also called restenosis, and a seriously reduced blood flow. In fact, clinically evident restenosis occurs in 30-40% of cases following successful PTCA and is most frequently observed between 3 and 6 months after the procedure. Late restenosis in the months after angioplasty reduces the initial success rate of 90% to 60-70% after six months. Although the incidence of success and associated complications has improved significantly over the last decade, the risk of restenosis has not changed. Hence, of the more than 300,000 coronary arteries subjected to angioplasty during 1990, 30-40% can be expected to restenose. As a result, there is a definite need for a method to reduce this high incidence of restenosis.
As the statistics demonstrate, restenosis after PTCA is a serious problem, and to date, there is no treatment to prevent this complication. It appears to be an inherent reaction of the vessel wall to the angioplasty stretching insult. The outward compression caused by the balloon catheter produces cracking, tearing, and stretching of the wall and a subsequent chain reaction of healing events. In short, it is believed to be caused chiefly by the migration and proliferation of smooth muscle cells which produces an exaggerated healing response. This response can progress to the point of severe restenosis and even occlusion. Due to this restenosis, at least one-third of all PTCA patients return for a second and even a third procedure. Accordingly, there is a definite need to decrease this high incidence of restenosis and thereby increase the long-term benefits of PTCA.
Two (2) approaches are currently employed to reduce restenosis. One approach involves the use of a revascularization device, such as the laser catheter, thermal catheter or stent to debulk plaque and create a smooth lumen to minimize turbulence and platelet aggregation along the vessel wall.
Another approach to reduce restenosis involves infusing a drug which modulates cell growth into the target artery before, during, or after the angioplasty to inhibit the profileration of smooth muscle cells. In particular, antiplatelet agents such as aspirin and dipyridamole, and anticoagulants such as heparin, have inhibited platelet aggregation and thrombus formation to a limited degree, thereby reducing the risk of early occlusion. There is therefore a critical need for an effective method to prevent and/or minimize restenosis after an intravascular procedure. The present invention satisfies this need and provides related advantages as well.
Radiation is used to treat cancer and other diseases of the body. Radiation has long been proven to destroy fast multiplying cells (e.g., cancer) in hopes of destroying or preventing the spread of the disease. Brachytherapy, which is the treatment of cancer at close distances, is one example of the use of radiation for treating diseases of the body. During brachytherapy, a radioactive source or sources are positioned in the area needing treatment. Depending on the shape, size and delivery means of the radioactive sources, the sources are either kept permanently in the body or removed after a specific amount of time. Since permanent implants are tiny seeds approximately 3 mm long and 0.5 mm wide, the use of these seeds do not relate to the present invention. Consequently, the focus of this application will be on the field of temporary implants.
The term temporary implants describes the procedure of maneuvering a radioactive source or sources to the treatment site utilizing a transport catheter or tube which has been previously placed in the vicinity of this treatment site. Alternatively, the transport catheter and temporary implant can simultaneously be maneuvered to the treatment site. In either situation, after a specified period of time, these sources and the transport catheter or tube are removed from the body. Since the radioactive source or sources may encounter a tortuous path in various arteries, veins, ducts, or the like inside the body to reach the treatment site, the radioactive source is usually attached by some device to a flexible drive member. This source and the drive member may be used many times, and, therefore must be able to withstand the many bends it encounters when it is maneuvered to the treatment site or removed therefrom, without breaking.
There are several devices on the market in which radioactive sources are attached to flexible drive members. Each of these devices is constructed in a different fashion and each has its limitations. Examples of these prior art devices are described in U.S. Pat. Nos. 4,819,618 and 5,141,486, both issued to Liprie as well as U.S. Pat. No. 4,861,520 issued to van""t Hooft. The two Liprie patents describe a radioactive element which is attached to a drive member by means of a junction welded to the drive table. The patent to van""t Hooft describes an apparatus which attaches radioactive sources to a drive cable by means of a stiff capsule welded into the end of the cable. Since the most resistive portion to flection of any flexible material, such as a cable, tube, or wire is the segment closest to the end, to join a capsule which is stiffer than this material and welded onto its end would only add to the resistance to bending and would adversely effect maneuvering the material through the body.
U.S. Pat. No. 5,084,002 issued to Liprie describes an ultra-thin high dose iridium source included within an oversized hole drilled inside the end of a solid platinum wire. Drilling a hole into a thin wire is very difficult since the maximum depth the hole can be drilled is equal to approximately seven times the outside diameter of the wire. To drill a hole deeper than this is extremely difficult due to the drifting of the drill as it burrows the hole. This drifting can lead to a thinning of the cavity walls which greatly increases the chances of breakage. This breakage is often disastrous, resulting in unwarranted radiation exposure. A larger outside diameter wire will be needed to compensate for the drifting and still allow the walls of the cavity to be thick enough to withstand stress. Unfortunately, this larger diameter wire might be too large to fit into many constricted areas of the body. As described in Liprie ""002 one can drill a cavity inside a solid wire, if one starts with an oversize wire and an oversize hole and then the whole assembly is drawn down to the desire diameter of the wire. However, whenever a wire is drawn down, the assembly containing the cavity elongates and the precise positioning of the radioactive core inside the assembly can become very difficult. Additionally, this larger diameter wire would result in less flexibility and may not be able to be maneuvered to the treatment site.
Finally, U.S. Pat. No. 5,282,781 issued to Liprie employs tube, a backbone wire, a pure iridium core and a plug and draws down the entire assembly to form a tight seal between the housing material and the backbone wire and the plug. Without this drawing down of the housing onto the backbone wire, radioactive flakes from the core would migrate throughout the inside of the assembly wire, resulting in unwanted contamination. This xe2x80x9cdrawing downxe2x80x9d step would increase the costs and difficulty of manufacturing the source wire. Furthermore, any xe2x80x9cdrawing downxe2x80x9d step as described in U.S. Pat. No. 5,084,002 and U.S. Pat. No. 5,282,781 would not work on a memory resistant alloy. As soon as a memory resistant alloy had been drawn through a die, the alloy would resume its original shape. If the memory resistant alloy was drawn beyond the threshold of its elasticity, then the memory resistant properties of the alloy would be destroyed.
Thus, there exists a need for a radioactive source wire that has an extremely small diameter and is flexible, yet has sufficient tensile strength to traverse a tortuous route of bends and turns without breaking.
It is an object of the present invention to provide a small diameter source wire that is extremely flexible and will allow the source to travel to the site of treatment without binding.
It is another object of the present invention to provide a source wire that is strong enough to withstand the stresses placed upon the source, as it is maneuvered to and from the site of treatment within the patient, without breaking.
Yet another object of the present invention is to provide an improved source wire design that includes a mechanism for relieving some of the stress encountered by the metal housing tube of the source wire as it is maneuvered to the treatment site.
Still yet another object of the present invention is to provide an improved source wire that exhibits little or no memory retention when bent.
These and other deficiencies of the prior art are addressed by the present invention which is directed to a flexible source wire for the radiation treatment of disease in which the source wire contains a radioactive core and is easily maneuvered to the site of treatment through various conduits in the body.
One general embodiment of the source wire of the present invention includes a thin, generally cylindrical, elongated, flexible housing tube having a distal end and a proximal end. The housing tube further comprises an unmodified section at its distal end and a modified segment at its proximal end, where the wall thickness of the modified segment is thinner than the wall thickness of the unmodified section. A plug seals the lumen of the unmodified section from the lumen of the modified segment which contains a radioactive core. Both ends of the source wire are sealed and at least the proximal end is rounded to ease its movement through the tortuous bends and turns as it travels to the treatment site.
An alternative embodiment of the source wire has a tapered section, having a tapered internal diameter that goes from the larger internal diameter of the modified segment to the smaller internal diameter of the unmodified section. Other embodiments may also include a backbone wire that extends throughout the unmodified section to the tapered section. Preferred embodiments of the present invention will have a housing tube and a plug constructed from a material exhibiting little or no memory retention when bent.
The flexible source wire described herein may have a backbone wire or plug that is tapered at the end closest to the radioactive core. The tapered end of the backbone wire or plug terminates next to the radioactive core in a rounded area shaped like a ball. The radioactive core, positioned within the proximal end of the housing tube, may exist openly within the housing tube or may be localized in an open-ended capsule or may be encapsulated by a thin-walled, flexible material or coating that allows the passage of neutrons.
One advantage of the present invention is that it can be made with a smaller diameter housing tube than the source wires that are currently available.
Another feature and advantage of the present invention is that the source wire has a sufficient tensile strength and flexibility to withstand the stresses encountered when the source wire is maneuvered to the site of treatment.
Yet another feature and advantage of the present invention is that it provides a novel mechanism for transferring the stress encountered by the metal housing tube as the source wire is maneuvered to the treatment site from the weakest portion of the source wire to the strongest portion of the source wire.
Still yet another feature and advantage of the present invention is that the source wire is made of a material that can undergo a 1% strain with less than a 1% alteration in its original conformation.
Another feature and advantage of the present invention is that the source wire will exhibit flexibility similar to a tube and have the tensile strength properties closer to a solid wire.
An additional feature and advantage of the present invention is that the radioactive source is visible with a fluoroscope.
Another feature and advantage of the present invention is that the radioactive material of the radioactive source is sealed within the proximal end of the source wire.
Still yet another feature and advantage of the present invention is that the radioactive source is long enough to treat the entire length of an angioplasted vascular stenosis.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.